FIG. 1 depicts schematically parts of a power train for a motor vehicle 1, e.g. a passenger car or a heavy motor vehicle such as a truck or bus. The power train comprises an engine 10 which in this case is mechanically connected by a shaft to a first end of a gearbox 20 via a clutch device 40. The gearbox 20 has its second end mechanically connected by a propeller shaft 50 to a differential gear 30 associated with a rear axle. The rear axle comprises left and right drive shafts 60 which drive the undepicted powered wheels of the vehicle 1.
By this well-known arrangement the mechanical work of the engine 10 is transferred, via a number of transmission devices such as clutch device 40, gearbox 20, propeller shaft 50, differential gear 30 and drive shafts 60, to powered wheels for propulsion of the vehicle 1. The gearbox 20 is a transmission device which has a number of forward gears for propelling the vehicle 1 forwards and usually also one or more reverse gears. The number of forward gears varies but twelve forward gears are for example usual in trucks of more modern kinds.
The transmission ratio of a power train may vary, enabling it to assume various ratios (i.e. various transmission ratio configurations). The various ratios depend inter alia on the gear currently engaged in the gearbox 20 and on the ratio of the differential gear 30. It may further be noted that there are power trains which can assume a number of different discrete transmission ratios and also power trains which have a continuous range of ratios, e.g. automatic gearboxes 20 with so-called converters or other types of gearboxes 20 with continuously variable transmissions.
In addition, most motor vehicles 1 have a control system comprising one or more electronic control units 110 (ECUs). The purpose of said control system is to control/regulate one or more functions in the vehicle 1, e.g. by means of one or more actuators which may be related to various functions in the vehicle 1, such as engine control, gear changing, cruise control, suspension configuration, etc., and said control system uses a number of different parameters, e.g. current engine speed, current accelerator pedal position, current engine torque, and data from various sensors, to control the various functions of the vehicle 1. These parameters are therefore used as input parameters in the control system for controlling the various functions in the vehicle 1.